This book constitutes the refereed proceedings of the 11th International Conference of the Italian Association for Artificial Intelligence, AI*IA 2009, held in Reggio Emilia, Italy, in December 2009. The 50 revised full papers presented together with 3 invited talks were carefully reviewed and selected from 83 submissions. The papers are organized in topical sections on knowledge representation and reasoning, machine learning, evolutionary computation, search, natural language processing, multi-agent systems and application.